1. Field
The disclosed subject matter relates to a multi-color image-forming apparatus. In particular, the disclosed subject matter related to an image forming apparatus that detects the positions of ink, toner and the like in order to reduce the shift of printing position for each color (C (cyan), M (magenta), Y (yellow) and K (black)) when performing color printing by, for example, superposing the print of the colors.
2. Description of the Related Art
Conventionally, a method of correcting color shift using a CCD sensor has been known for multi-color image-forming apparati. FIG. 9 shows an example of a conventional multi-color image-forming apparatus that includes a transfer belt 90 and a CCD sensor 91 installed above the transfer belt 90.
Then, a positioning pattern 92 including each color C (cyan), M (magenta), Y (yellow) and K (black) is formed on the transfer belt 90 and, as shown in FIG. 9, irradiating light from an irradiation lamp 93 irradiates the positioning pattern 92. Reflected light is then read by the CCD sensor 91.
It is possible to use light in an infrared region (750 to 950 nm) as the irradiation light from the irradiation lamp 93 irradiating the positioning pattern 92. This is because the reading of the positioning pattern 92 can be detected at substantially the same sensitivity for each color.
The reflected light read by the CCD sensor 91 as described above is input to an MPU (main/central processing unit) and processed. The position of the positioning pattern is determined by the MPU, and the shift amount of registration is calculated. At this point, the transfer position of the positioning pattern is known, and transfer is performed by an instruction from the MPU when it is judged that the registration is in an allowable range by the MPU.
If it is judged by the MPU that the registration has deteriorated and exceeds an allowable range, the MPU calculates the error to find a shift amount. Then, a reflection mirror in a photosensitive optical path is activated by using a stepping motor in response to the shift amount to perform adjustment of at least one tilt in a sub-scanning direction, adjustment of parallel movement, or the like, and registration at the time of exposure by laser beam is matched. At this point, since the CCD sensor 91 can detect adhesion concentration as well, the same sensor combines the detection of position and adhesion concentration. (For example, see Japanese Patent Registration No. 2573855 gazette).
However, in the case of performing the positional detection of the pattern for each color (CMYK) by using the CCD sensor 91 as described above, there are several associated problems/drawbacks. For example, the CCD sensor 91 is expensive. In addition, the volume of data that is output from the CCD sensor 91 is enormous, requiring a high-speed MPU. In addition, a light source such as an infrared light source, for example, is also required because the CCD sensor 91 itself does not have a light source.